The invention relates to a suspension friction control assembly and friction control device for vehicles, particularly heavy commercial vehicles, which provide low or negligible friction for small movements of the suspension but higher frictional forces for large deflections of the suspension.
In known leaf spring vehicle suspensions, the friction between the spring leaves and between the springs and their mountings has both advantages and disadvantages, especially when applied to heavy commercial vehicles. There are existing devices for increasing and/or decreasing this friction for different applications, although such devices tend to be a compromise, providing the higher or lower friction characteristic over the whole range of suspension deflections.
Low friction improves the isolation ride of a vehicle, especially at small load variations or deflections. For instance, when travelling on a relatively smooth road, any static friction tends to lock the suspension up, with small input variations causing the tires of the vehicle to deflect. As the vehicle tires are virtually undamped, the vehicle tends to oscillate on the tires, thereby providing an unpleasant ride.
A disadvantage with known low friction control, leaf spring suspension is that sophisticated, highly durable dampers are required to control adequately the motions of the vehicle. To be fully effective, such dampers ideally require various settings to suit the different loading conditions to which the suspensions are subjected. Also, with low friction control, leaf spring suspensions, the rate of the vehicle movement, especially in the roll mode, is generally too high under the dynamic loadings which occur when the vehicle is manoeuvring. This often necessitates the use of stabiliser/anti-roll bars which tend to reduce the quality and comfort of the vehicle ride by stiffening the wheel rate when only one wheel is deflected.
On commercial vehicles, where the distribution of load between axles varies considerably in dependence upon the particular application, a high friction spring arrangement tends to dampen any actual frequency combinations which can cause severe ride and handling problems. Therefore, high friction spring arrangements tend to be more adaptable over the practical ranges of vehicle applications.
The present trend for leaf spring suspensions is towards spring leaves of parabolic tapering thickness which can be designed to produce more durable assemblies, but which tend to have low inter-leaf friction. As indicated above, this tends to give, on the one hand, advantages in the vehicle ride for small input variations but, on the other hand, the disadvantages discussed above for larger deflections.
An attempt has been made to overcome the disadvantages of suspension friction by providing between those parts of a spring which need to contact each other, but which also need to slide with respect to each other, such as the spring and its mounting and/or adjacent spring leaves, an elastomeric member. By a "shearing" action, the elastomeric material of such a member is able to accommodate the differential sliding motion between the spring and its mounting and/or adjacent spring leaves. However, these shear deflection members also suffer from the disadvantages of the lower friction, similar to those discussed above.
Accordingly, it is an object of the present invention to provide, a vehicle suspension incorporating a friction control device which overcomes, or at least substantially reduces, the disadvantages associated with the know suspension arrangement discussed above.
Thus, one aspect of the invention provides a vehicle suspension friction control assembly comprising a vehicle suspension having at least two components which are movable with respect to each other in the fore-and-aft direction of the suspension, and of which at least one component is a spring leaf, and a friction control device including a resiliently deformable member which is located between at least two of the suspension components and means for limiting deformation of the friction control member in the fore-and-aft direction of the suspension to a predetermined limited degree which is less than the inherent deformation limit of the resiliently deformable member, wherein the spring leaf and another of the suspension components are movable with respect to each other against sliding friction in said fore-and-aft direction subsequent to the member having been deformed to said predetermined limited degree.
Preferably, the means for limiting deformation of the member to said predetermined limited degree defines a positive stop therefor. Also, the deformation limiting means may include means for effecting a progressively increasing resistance to deformation of the member, terminating in a positive stop therefor.
In a preferred embodiment of inventive assembly, the friction control device includes a pair of generally parallel plates between which the resiliently deformable member is secured and of which one of the plates is in engagement with a spring leaf, and wherein said deformation limiting means includes respective means arranged on the plates to interengage with each other when the friction control member has been deformed to its predetermined limited degree, which defines a positive stop therefor, and whereby any subsequent relative movement between the spring leaf and the other suspension component in the fore-and-aft direction of the suspension is against sliding friction between the spring leaf and said one plate of the friction control device. The plate interengagement means may comprise opposed ends of each plate being bent inwardly with respect thereto, such that corresponding pairs of respective bent plate ends can interengage, to provide said positive stop when the member has been deformed to its predetermined limited degree. Progressively increasing resistance means can compromise a resiliently deformable element arranged to act between the plates, in which case, the resiliently deformable element may be arranged to act between respective cooperating pairs of interengageable bent plate ends.
In another embodiment, the resiliently deformable member is secured directly to a first one of the suspension components and to a plate, another suspension component and the plate being slidable with respect to each other against friction when the deformable member has been deformed to its predetermined limited degree. The other suspension component may be a spring leaf of the suspension. Also, the suspension component to which the member is secured directly may be another spring leaf of the suspension.
At least two components of the vehicle suspension may be respective leaves of a multi-leaf spring of which at least one is arranged to slide in frictional engagement with a corresponding one of the pair of parallel plates of the friction control device when the member has been deformed to its predetermined limiting degree.
Means may be used to clamp the leaves of the multi-leaf spring together, with another resilient element located between the clamping means and at least one of the spring leaves. The other resilient element may be secured to a clamp plate of the clamping means.
In another embodiment, the vehicle suspension comprises a cam spring suspension arrangement with the resiliently deformable member being secured between confronting faces of upper and lower components of a frame mounting bracket of the cam spring suspension arrangement, and wherein the lower frame mounting bracket component is arranged upon the spring leaf of the suspension, such that relative movement between the frame mounting bracket and spring leaf which would otherwise cause further deformation of the resiliently deformable member beyond said predetermined limited degree, causes slide motion, against friction, between the lower frame mounting bracket component and the spring leaf.
In a further embodiment of the invention, the vehicle suspension comprises a pair of spring leaves with the friction control device located therebetween, the spring leaves and the friction control device being secured together by an elongate clamping member passing through respective holes in the leaves and device with clearance between the elongate clamping member and the respective peripheries of the hole in the device and the hole in at least one of the spring leaves, the clearance, in the fore-and-aft direction of the suspension, between the elongate clamping member and the periphery of the hole in the least one spring leaf being greater than that between the elongate member and the periphery of the hole in the friction control device, the deformation limiting means being defined by the elongate clamping member and the periphery of the hole in the friction control device with which the elongate clamping member engages when the resiliently deformable member has been deformed to the predetermined limited degree, at least one of the spring leaves being movable with respect to each other in the fore-and-aft direction of the suspension against sliding friction between the at least one spring leaf and the friction control device when the resiliently deformable member has been deformed to the predetermined limited degree.
Again, the friction control device may include a pair of generally parallel plates between which the resiliently deformable member is secured. Also, only one of the spring leaves may have a hole with clearance between the elongate clamping member and the periphery thereof and the resiliently deformable member may be secured directly to the other spring leaf and to a plate which is slidable against friction with respect to the one of the spring leaves when the deformable member has been deformed to the predetermined limited degree. The spring leaves and friction control device may be clamped together by a pair of opposed clamping plates secured together in clamping relationship by the elongate clamping member. Preferably two elongate clamping members are used.
A second friction control device may be located between one of the spring leaves and the adjacent clamping plate and the resiliently deformable member of the second friction control device may be secured directly to the adjacent clamping plate.
Further, only one of the spring leaves may have a hole with clearance between the elongate clamping member and the periphery thereof, wherein the resiliently deformable member of the first friction control device may be secured directly to the second spring leaf and to a plate which is slidable against friction with respect to the first spring leave when the deformable member has been deformed to the predetermined limited degree.
The resiliently deformable member is preferably made of an elastomeric material which may be either natural or synthetic, or, indeed, any other suitable, resiliently deformable material.
In order that the invention may be more fully understood, preferred embodiments in accordance therewith will now be described by way of example and with reference to the accompanying drawings in which: